Current hypodermic syringes present a problem in that the sharp-pointed cannulas thereof frequently cause injury and infection subsequent to administration of medicinal fluid. Typically, a hypodermic syringe is used in the form of a disposable, preloaded syringe of plastic material having a barrel and a piston reciprocable by means of a plunger therein. A sharp-pointed cannula is normally fixed to the forward wall of the syringe barrel and protected by means of a removable plastic sheath. U.S. Pat. No. 4,317,446 to Ambrosio et al., for example, shows such a syringe.
A serious problem presented by many prior art syringes results from exposure of the protruding cannula after use. The person administering the injection may inadvertently become stuck by the contaminated cannula. This not infrequent incidence of contamination can cause the spread of various diseases, including hepatitis and acquired immune deficiency syndrome (AIDS). In addition to the serious danger posed to health care workers, such accidents are costly to hospitals and other medical facilities in terms of time and administration costs; typically, an incident report has to be filled out for each such inadvertent wounding.
One solution to this problem has been to cover the cannula after use with a cap-like "Luer-locking" ("Luer-Lok" is a trademark of Becton-Dickinson Co., Rutherford, N.J.) structure (see, e.g., U.S. Pat. No. 4,540,405 to Miller et al.). However, the possibility of inadvertent piercing of one's finger after injection remains. It is thus desirable to provide an alternative design of syringe so as to safely and easily prevent exposure of the needle after injection. U.S. Pat. No. 4,026,287, of common inventorship herewith and over which the instant device is an improvement, provides a proposed solution. In that patent, the disclosure of which is hereby incorporated by reference in its entirety, I proposed a syringe having a breakable end wall at the forward end of the syringe barrel, the cannula mounted on the end wall and severable therefrom upon retraction of the piston. The instant invention, while directed toward the substantially identical problem, provides a syringe which is easier and less costly to manufacture, having fewer parts and being of generally simpler design.